Fitness machines have been used by individuals to enhance their physiques, increase muscle strength, and improve overall health. At the same time, serious athletes that compete at professional or semi-professional levels also wish to use specialized training or fitness machines that tailor to their needs. This causes a concern whenever an individual moves from a casual fitness schedule to a more rigorous one: the less-intensive fitness machines need to be replaced because they can't adapt to the new routines of the individual. Current fitness machines or devices are designed as such so to encourage individuals to purchase new ones.
At the same time, existing fitness machines can't be used as a rehabilitation device due to the structure and limitations of existing fitness machines. Again, if an individual desires to have a rehabilitation device, one could not convert the existing fitness machine for that purpose.